During this time, the ICO conducted an investigation into allegations that Google had knowingly gathered personal data while collecting photographs as part of its Street View mapping project.

The ICO ruled that there had been a "significant breach" of the Data Protection Act, but opted not to fine the company, a decision heavily criticised by campaign group Privacy International and others.

Of the 2010 investigation, deputy information commissioner David Smith told the BBC: "We spent less time searching than others did. If we had searched for days and days we would have found more."

It later emerged that several Google staff had been told that data was being collected, prompting the ICO to reopen its inquiries.

Email correspondence

The documents, obtained by campaigner Peter John, showed Mr McCartney had outlined what he had said were "significant errors" in the media's reporting of the issue in an email dated 4 May 2012.

Christopher Graham, the information commissioner, responded to the email with "thanks for this, Stephen".

In a statement released today, the ICO said: "The published correspondence between Google and the ICO clearly shows that Stephen McCartney was treated like any other organisation's representative, with his emails receiving nothing more than a polite acknowledgement.

The spokesman added: "ICO employees continue to be legally bound by a confidentiality agreement after they leave the organisation, as part of the Data Protection Act.

"Stephen Eckersley, the ICO's Head of Enforcement, continues to investigate Google's actions with regard to the Street View project."

Mr Eckersley is currently considering a response to
Google's most recent letter
on the matter which was received by the ICO last month.